The present invention was developed to improve the manufacture of semiconductors. The semiconductors are formed from "wafers" that are substantially planar-shaped fragile objects. These wafers are retained in slotted trays during the semiconductor manufacturing process. Because the wafers are constructed of thin, brittle, and expensive material, they must be carefully handled and stored.
One method for storing such objects is to place them in a tray having a plurality of slots that are sized and shaped to receive the planar-shaped objects. The slots are evenly separated by spaces to permit a robotic arm to insert the objects in the tray and remove them therefrom. The tray has a first opening sized and shaped to permit the objects to be inserted into and removed from the slots in the tray. One recurring problem is the misplacement of the objects in the tray such that one side of the object is received in one slot and the other side of the object is received in an unmatching slot, resulting in a "cross-slotted" condition. In this condition, the object is disposed across one or more spaces separating the slots.
When cross-slotting occurs, the attempt to insert additional objects into a slot occupied by a cross-slotted object will result in breakage of one or both of the objects. This is undesirable because not only are valuable objects destroyed, but the manufacturing process must slow down or come to a halt while the broken debris is removed and the cause of the cross-slotting remedied.
Another recurring problem is the tendency of objects received in the trays to slide at least partially and sometimes entirely out of the slots. Again, this can result in breakage and a resulting slowdown in the manufacturing process.
Hence, there is a need for a method and apparatus that maintains the objects in the slots during the manufacturing process and that detects and prevents cross-slotting of objects before breakage occurs. Ideally, the detection of cross-slotted objects will include notification to a controller for immediate remedial action, which will result in preventing the unnecessary breakage of objects and interference with the manufacturing process. "Controller" as used herein includes human operators as well as electronic and robotic devices that control the insertion and removal of objects in the tray.